Refrigerating apparatus



s Sheets-Sheet 1 Filed May 14, 1947 IIIIIIIIIIII Den/:0 flag/001v.

Nov. 2, 1948. D. ARONSON REFRIGERATING APPARATUS 3 Sheets-Shea; 2-

Filed May 14, 1947 E E E E E E E Davza flnolvsolv.

Patented Nov. 2, 1948 REFBIGERATING APPARATUS David Aronson, Greensburg, Pa., asslgnor to Elliott Company, Jeannette, Pa., a corporation of Pennsylvania Application May 14, 1947, Serial No. 748,079

My invention relates to refrigerating apparatus in which a primary refrigerant having a very low boiling point, such. as liquid air, is used to cool a secondary refrigerant that is a highly volatile fluid and that is circulated as a heat transfer agent between the primary refrigerant and a refrigerator compartment, More particularly my 8 Claims. (Cl. 257-3) may be a liquid that undergoes no change of state.

invention relates to an improvement in apparatus of this type for use in a railroad car, or other vehicle or vessel, carrying perishable products that require refrigeration in transit.

Proper refrigeration of such perishable prod- .ucts demands a refrigerating system that is capable of providing the wide range of low temperatures'required by various products, including frozen foods that must be kept at low or sub-zero temperatures, and that at the same time is capable of maintaining those required temperatures within very narrow limits. Such flexibility over a wide temperature range and such closecontrol of temperatures within that range are not adequately provided by conventional refrigerants and refrigerating apparatus operating without a source of external power.

Liquid air has frequently been proposed as a refrigerant for preserving perishable products in transit. It boils, however, at so low a temperature (around 308 F.) relative to the desired temperature in the refrigerator compartment, that cooling'by liquid air alone has serious disadvantages. For example, if the heat exchanging surfaces within the compartment are cooled directly by liquid air, they become so cold that the air within the compartment is almost completely dehumidified, resulting in a large accumulation of frost on those surfaces and possible injury, from dehydration, to the products being shipped. If vaporized liquid air is blown directly into the refrigerator compartment, other difficulties are encountered. Among them, is the fact that as the liquid air evaporates in its container the oxygen content of the resulting vapor will increase (by reason of the more volatile nitrogen tending to vaporize first) to an extent that is injurious to many food products and that may create an explosion hazard.

It has been suggested that these disadvantages might be overcome by circuating a secondary refrigerant as a heat-transfer agent between the liquid air and the refrigerator compartment, so that there would be a large diflerence in temperature between the primary and secondary refrigerants buta relatively small difference in temperature between the secondary refrigerant and the compartment. The secondary refrigerant or it may be a highly volatile fluid that has a boiling point between the temperature of the primary refrigerant and the temperature that it is desired to maintain within the compartment.

Refrigerating systems heretofore proposed that embody the foregoing suggestion retain, however, several disadvantages that make th'em'inemcient and, because of the high cost or liquid air, uneconomical. Where the secondary refrigerant is a liquid, such as brine, that undergoes no change of state, a considerable quantity of the liquid must be circulated to absorb a given amount of heat from the refrigerator compartment. In addition, since the liquid becomes progressively warmer as it flows through the system, it is dimcult to control the temperature of the compart ment within the narrow range that is so desirable in shipping some perishable foodstuffs. Where the secondary refrigerant is a highly volatile fluid that does undergo a change of state, the volume of liquid required is much smaller, because most of the fluid is circulated in the form ofvapor. Moreover, by using such fluids it is possible to "take advantage of their high heat absorbing capacity when passing from a liquid to a vapor state without change in temperature. Nevertheless, no system to my knowledge has so far been devised in which full advantage is taken of the latent heat of evaporation of volatile fluids and in which it is possible to control the temperature of the refrigerator compartment within very narrow limits.

It is among the objects of my invention to provide a refrigerating apparatus of the t described, in which a secondary refrigerant consisting of a. highly volatile fluid is circulated in a closed circuit as a heat transfer agent between a primary refrigerant having a very low boiling point and a refrigerator compartment and in which the secondary refrigerant ls evaporated without substantial change in temperature throughout practically all of the circuit that is in heat exchange relation to the compartment, thereby obtaining very high efilciency in the absorption of heat from the compartment and permitting the temperature therein to be maintained practl-callyconstant.

Another object of my invention is to provide, in conjunction with refrigerating apparatus of the type described, means by which the temperature of a compartment may be maintained at a predetermined level even when that level is above the temperature of. the air outside of the compartment.

In accordance with my invention, a highly volatile fluid is circulated as a secondary refrigerant in a closed circuit in heat exchange relation both to a primary refirgerant having a very low boiling point and to a refrigerator compartment. The volatile fluid is initially condensed to a liquid in a condenser by giving up heat to the primary refrigerant. The liquid is then evaporated by heat absorbed from the compartment, the resulting vapor being led back to the condenser and recondensed. Continuous circulation of the fluid is maintained without a pump by the difference in density between its vapor and liquid states. The primary refrigerant, which is preferably liquid air, is stored in a tank outside of the compartment. It flows from the tank at a controllable rate to a vaporizer, which is preferably a coil within the condenser, and is there vaporized by heat absorbed from the circulating fluid. The warm vaporized air is then discharged into the atmosphere.

1 The heat exchanging surfaces within the compartment that are in direct contact with the circulating fluid consist almost entirely of numerous upwardly extending evaporator tubes and of metal plates that engage the tubes and increase the flow of heat to them. These tubes are adapted to receive the circulating fluid in a liquid state at their lower ends. They are of such diameter that vapor resulting from the evaporation of liquid therein forces unevaporated liquid upwardly, thereby causing liquid to evaporate throughout their length. If this liquid has not been subcooled below its boiling point, all of the heat absorbed by it will -be used to change it from a liquid to a vapor state, without change in temperature. Since this change of state takes place approxiprotective doors removed; and Fig. is an en- I larged detail of an evaporator tube taken on the mately uniformly throughout the compartment,

the heat exchanging surfaces therein are kept at a substantially uniform temperature, thereby permitting the temperature in the compartment to bemaintained within a very narrow range.

When it is desired to maintain a temperature in the compartment that is above the temperature of the air outside, as will often be thecase in cold weather, heat must be supplied to the compartment instead of refrigeration. The necessary heat can be provided and efllciently transferred to the compartment by a burner in heat exchange relation to the liquid in the circulating system. The liquid is thereby evaporated, and the resulting vapor flows in a reverse direction through the circuit, that is. down instead of up in the evaporator tubes. The vapor gives up heat in the tubes to the compartment and is thereby condensed. to a liquid. Again, the heat exchange between the circulating fluid and the compartment takes place approximately uniformly throughout the tubes and is accompanied by a change of state in the fluid without change in temperature, thereby warming the compartment uniformly and permitting the temperature therein to be maintained within a very narrow range.

This invention is particularly useful in connection with railroad refrigerator cars using liquid air as the primary refrigerant. It is to be understood, however, that my invention is equally applicable to other vehicles or vessels and to other refrigerants having a very low boiling point,

In the accompanying drawings, Fig. 1 is a fragmentary plan view of a railroad car, with the roof removed, embodying my invention; Fig. 2 is a fragmentary vertical section of the car along the line II-II in Fig. 1: Fig. 3 is a vertical section along the line IIIIII in Fig. 1; Fig. 4 is a fragline VV of Fig. 2.

Referring to the drawings,-the walls, roof, and floor of a refrigerator car are represented by i, 2, and 3, respectively. They are preferably insulated with rock wool, or other suitable material, to reduce the transfer of heat betwen the car and the outside air. A partition 4 divides the car transversely into a refrigerator compartment 5 and a refrigerant chamber 6. The latter is provided with one or more storage tanks 1 for holding liquid air. Two such tanks are shown in the drawings, and they are connected near their bottoms by a pipe 8 to maintain the liquid air in each atthe same level. Each tank is provided with a filler pipe 9 for introducing liquid air, and these pipes extend almost to the bottom of each tank to reduce splasing during the filling operation. The filler pipes also extend through the roof of the car, where their upper ends are protected by hatches ill, provided with removable lids. Any moisture entering the hatches is .drained by pipes ii that discharge through the floor of the car. Surrounding the upper part of each filler pipe and spaced from it is a casing l2, to the upper end of which is attached a removable cap l3 with small vent holes around its side. The annular space between the casing and flller pipe permits air to escape from the tank while the latter is being filled with liquid air. That space and the vent holes in the cap it also permit the escape of air that is continually vaporized within the tank by unavoidable heat leakage from outside, thereby preventing dangerous pressures from developing in the tank. To equalize such pressures as may develop in the main body of the tank and in the filler pipe, radial openings 40 are provided in each filler pipe below the top of the tank. These holes and the annular space between the flller pipe and casing provide a communicating passage for vaporized air. When the liquid level in the tank is above the bottom of the casing a similar communicating passage may be created by providing radial openings in the casing.

Liquid air is conducted from the bottom of each tank through pipes id to a vaporizer i5, which is in heat exchange relation to a secondary refrigerant in a condenser iii. The vaporizer is shown in its preferred form as a coil within the condenser, but could take other forms that provide a heat conducting surface of proper area. The lower portion of the vaporizer coil is preferably as low as the bottoms Of the tanks 7, in order that liquid ai will always flow from the tanks to the coil, even when the tanks are nearly empty. Liquid air entering the.bottom of the vaporizer is boiled as it rises throughthe coil by heat absorbed from the secondary refrigerant admitted to the top of the condenser. sorbs heat from the secondary refrigerant and is finally vented to the atmosphere through a pipe ll, after it has been warmed to a temperature only slightly below that of the secondary refrigerant.

The secondary refrigerant is a highly volatile liquid that flows in a closed circuit as described below. In one part of the circuit it is a liquid, in another part it is a vapor changing from one state to the other at a rate determined by the amount of heat that it absorbs from or gives up to its environment in a given time. If the liquid is .not subcooled, the temperature of the fluid throughout the circuit will be substantially uni- The resulting vaporized air also ab-.

form and will correspondto the'boiiing point of I .other well-known refrigerants may be used that have a boiling point between that of the primary refrigerant and the temperature that it is desired to maintain in the refrigerator compartment. Thefiuid enters the top of condenser 18 as a vapor, and this vapor is cooled. and condensed bygiving up heat to the liquid and vaporized air as previously'described. The resulting liquid collects at the bottom of, the condenser. To avoid subcoollng of this liquid, the bottom of the condenser is preferably lower'than the vaporizer,

so that enough liquid may accumulate between- 'ends of the tubes are connected to vapor return pipes 20 that are near the roof of the car.

To increase the flow of heat from the compartment to the secondary refrigerant within the tubes, the latter engage metal plates 2| covering the inner surface of the side walls of the compartment. The tubes are preferably placed within folds in the plates, which open towards theside walls of the car and almost completely surround the tubes. This means of engaging the tubes and plates not only assures good thermal contact between them, but also provides the tubes with considerable protection against physical injury when the car is being loaded and unloaded. The tubes may be further protected by vertical shielding sheets 22 of any suitable material, held by studs 23 close to but spaced inwardly from the plates 22, and also spaced from the floor and roof of the refrigerator compartment. The sheets 22 perform another useful function in directing the flow of air from the top of the compartment downward between the sheet and the adjacent plate and out between-the bottom of the sheet and the floor.

The evaporator tubes is have an internal diameter that is sufficiently small to cause vapor resulting from the evaporation of liquid therein to entrain unevaporated liquid and carry it upward in the tubes to evaporate at a higher level than otherwise would be the case if tubes of a larger diameter were used. By the proper selection of tube size, the evaporation of the liquid entering the lower ends of the tubes from pipes l8 takes place approximately uniformly throughout the length of the tubes. The resulting vapor is led by the return pipes at back to the upp r end of the condenser. Circulation of the secondary'refrigerant in this closed circuit is maintained without a pump by the difference in density between its vapor and liquid states.

Because the evaporator tubes and the metal plates engaging them provide the principal cooling surfaces within the compartment, substantially all of the. heat that is absorbed by the fluid from the compartment is absorbed in those tubes. Because the evaporation of liquid within the tubes takes place approximately uniformly throughout their length, substantially all of that heat is used to change the fluid from a liquid to a vapor, without change in temperature. As

a result, the'cooling surfaces are kept at a substantially uniform temperature that corresponds to the boiling point of the fluid, and the compartment is likewise kept. at a substantially uniform temperature that is slightly higher than the temperature of the cooling surfaces.

-The boiling point of the circulating fluid is determined, as previously stated, by the characteristics of the fluid and-its pressure. In using dichloro-diiluoro-methane as the circulating fluid, the pressure in the system that is required to provide suitable refrigeration over the usual temperature rangeis about 85 pounds per square inch absolute when the fluid (entirely in the vapor state) is at a temperature of 70 F. As part of the vapor is condensed, the pressure of the remaining vapor and the boiling point of the liquid arelowered until a state of equilibrium is reached in which liquid evaporates in the evaporator tubes at the same rate as vapor is condensed in the condenser. In normal operation, this state of equilibrium is reached before the liquid in the bottom of the condenser rises high enough to come into contact with the vapoa rizer, thereby avoiding any subcooling of that liquid. Appreclable subcooling of the liquid (1. e. cooling it well below its boiling point) may lower the temperature of the heat exchanging surfaces 'in the compartment to a point that will cause the condensed in the condenser and the liquid level therein rises (until equilibrium is restored by increased evaporation of the liquid), thereby reducingthe pressure of the circulating fluid and lowering its boiling point. The temperature within the compartment may, accordingly, be regulated within desired limits by controlling the flow of liquid. air to the vaporizer. That flow may be suitably controlled by a valve 24 preferably placed at the discharge end of pipe ll leading from the vaporizer (see Fig. 4). This valve may be operated by a temperature responsive device 25 within the refrigerator compartment. When the temperature within the compartment drops below a predetermined level, valve 24 begins to close, permitting less liquid air to enter the vaporizer. .As a result, the rate of condensation and evaporation of the fluid is decreased and its temperature rises slightly. If the temperature in the compartment continues to decline, the flow of liquid air is entirely out 01f. When the temperature within the compartment rises above a predetermined level, valve 24 opens and permits a greater amount of liquid air to enter the vaporizer, thereby increasing the rate of condensation and evaporation of the fluid and slightthe pipes ll, in a region between the condenser It and theevaporator tubes. A preferred means for supplying such heat is illustrated in Pig. 4. A' valve 26, operated by a temperature responsive device 21 within the refrigerator compartment, admits fuel'to a pipe 28 which conducts it t a burner 29. The burner is in heat exchange relation to a pipe 30 that is connected to pipes l8 and 20 on one side of the car and (is so positioned denser to the lower ends of the evaporator tubes in the compartment.

3. Apparatus for cooling a refrigerator compartment in a vehicle or Vessel, com-prising upthat it is below the normal level of liquid in pipe 1 of the car gives up heat therein to the compartment, and is condensed to aliquid. This liquid trickles down the inside of the tubes to both of the pipes 18 which lead it to the condenser where it maintains the liquid level in pipe 30. When the burner is in operation, the compartment is warmed uniformly and economically because, as in the case of refrigerating the compartment, the circulating fluid undergoes a change of state that takes place approximately uniformly throughout the length of the tubes.

According to the provisions of the patent statutes, I have explained the principle of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, theinvention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. Refrigerating apparatus comprising spaced upwardly extending evaporator tubes for receiv--' ing at their lower ends a highly volatile liquid and having an internal diameter sufficiently small to cause vapor resulting from the evaporation of liquid therein to carry upward unevaporated liquid,

a conduit for withdrawing vapor from the upper ends of the tubes, a condenser for receiving vapor from the conduit, a vaporizer located within but spaced from the bottom of the condenser and adapted to receive a liquid refrigerant having a very low boiling oint, whereby the vapor in the condenser will be condensed to a liquid that collects in the bottom of the condenser without bein su bcooled by the refrigerant, and a conduit .for

wardly extending evaporator tubes adapted to be spaced along a side wall of the compartment for receiving at their lower ends a highly volatileliquid and having an internal diameter sufllciently 7 small to cause vapor resulting from the evaporation of liquid therein to carry upward unevaporat-ed liquid, a conduit for withdrawing vapor from the upper ends of the tubes and conducting it outside of the compartment, a condenser for receiving vapor from the conduit, a tank for a liquid refrigerant having a very low boiling point, a vaporizer in heat exchange relation to the condenser, a conduit connecting the tank to themporizer so that refrigerant will flow to the vaporizer and condense the vapor in the condenser to a liquid, a conduit for conducting the liquid from the condenser to the lower ends of the evaporator tubes in the compartment, and a valve adapted to respond to the temperature in the compartment tor controlling the flow of refrigerant to the vaporizer in accordance with that temperaturc.

, 4. Refrigerating apparatus for cooling a compartment, comprising upwardly extending evaporator tubes adapted to be spaced along a side wall of the compartment for receiving at their lower ends a highly volatile liquid, each tube having an internal'diameter that is sufllciently small to cause vapor resulting from the evaporation of liquid therein by heat absorbed from the compartment to carry upward unevaporated liquid, a metal plate adapted to extend along the side wall of the compartment and having spaced folds to receive and engage the evaporator tubes. a shielding sheet close to but spaced inwardly from the plate and also adapted to be spaced from the top and bottom of the compartment, a, conduit for withdrawing vapor from the upper ends of the evaporator tubes and conducting it outside of the compartment, a condenser for receiving vapor from the conduit and condensing it to a liquid, a tank for a liquid refrigerant having avery low boiling point, a vaporizenpositioned within the condenser and having its lowest point lower than the bottom of thetank but spaced above the bottom of the condenser to avoid subcooling of the liquid condensed therein, a conduit connecting the tank to the bottom of the vaporizer so that reconducting the liquid from thecondenser to the lower ends of the evaporator tubes.

2. Apparatus for cooling a refrigerator compartment, comprising a metal plate adapted toe-1;;

extend along a side wall of the compartment, 'a

shielding sheet close to but spaced inwardly from the plate and also adapted to be spacedfrom the top and bottom of the compartment, aplurality of spaced upwardly extending evaporator tubes engaging one side of the plat for receiving at their lower ends a highly volatile liquid and havconduit for conducting the liquid from the conto frigerant will flow to the vaporizer, a return conduit for withdrawing liquid from the bottom of the condenser and delivering it to the lower ends of the evaporator tubes, whereby the highly volatile fluid will circulate in the closed circuit at a substantially uniform temperature.

5. In an apparatus for regulating the temperature of a compartment in a vehicl or vessel by means of a highly volatile fluid that is circulated in a closed circuit, the combination comprising upwardly extending evaporator tubes spaced along a side wall of the compartment for receiving at their lower ends a highly volatile liquid and having an internal diameter sufiiciently small to cause vapor resulting from the evaporation of liquid therein to carry upward unevaporated liquid, a conduit for withdrawing vapor from the upper ends of the tubes and conducting it outside of the compartment, a condenser for receiving vapor from the conduit, a tank for a liquid refrigerant having a very low boilingv point. a vaporizer in heat exchange relation to the condenser, a conduit connecting the tank to the vaporizer so mined minimum, a normally inoperative heater in heat exchange relation to liquid in the closed circult, and means responsive to the temperature in the compartment for bringing the heater into operation when that temperature falls to a certain point below said predetermined minimum, whereby liquid will be vaporized and the resulting vapor will flow through the evaporator tubes in a reverse direction and be condensed therein by giving up heat to the compartment.

6. The combination with a railroad refrigerator car compartment of apparatus for regulating the temperature of the compartment by means of a highly volatile fluid that is circulated in a closed circuit, said apparatus comprising upwardly extending evaporator tubes spaced along each of two opposite side walls of the compartment for receiving at their lower ends a highly volatile liquid and having an internal diameter that is sufficiently small to cause vapor resulting from the evaporation of liquid therein by heat absorbed from the compartment to carry upward unevaporated liquid, whereby evaporation of liquid will take place approximatelyuniformly throughout the tubes, a metal plate, along each of the side walls of the compartment having spaced folds that partially surround and engage the evaporator tubes to increase the heat exchanging surface within the compartment, a shielding sheet close to but spaced inwardly from each metal and having its lowest point lower than the bottom of the tank but'above the normal level of liquid in the condenser to avoid subcooling of that liquid, a conduit connecting the bottom of the tank with the bottom of the vaporizer so that liquid air will flow tothe vaporizer and will there be vaporized by heat absorbed fromthe vapor in the condenser, two liquid conduits each connected to the bottom of the condenser for withdrawing the liquid therefrom and delivering it to the lower ends of the evaporator tubes along a different side wall of the compartment, a valve that is responsive to the temperature in the compartment for controlling the flow of liquid air to r the vaporizer in accordance with that temperawarming conduit having one end connected to plate and also spaced from the top and bottom of the compartment to protect the plates and the evaporator tubes from injury and to provide passages for air circulating in the compartment, two vapor conduits each connected to the upper ends of the evaporator tubes along a different side wall of the compartment for receiving vapor from those tubes and conducting it outside of the compartment, a condenser connected to both conduits for receiving the vapor therefrom and condensing it to a liquid, a tank for receiving liquid air, a

-vaporizer coil positioned within the condenser one of the liquid conduits for receiving liquid therefrom and its other end connected to one of the vapor conduits, a normally inoperative heater in heat exchange relation to the warming conduit .in a region below the normal level of liquid therein, and a valve that is responsive to the temperature in the compartment for admitting fuel to the heater and bringing the heater into operation when that temperature fails a predetermined amount below the temperature at which the flow of liquid air to the vaporizer is cut off, whereby the liquid that is warmed by the heater in the warming conduit will be vaporized and resulting vapor will be conducted through the adjacent vapor conduit to the upper ends of the evaporator tubes and in flowing down those tubes will be condensed to a liquid by giving up heat to the compartment.

' DAVID ARONSON.

nsrnnnncns crrsn The following references are of record in the file of this patent:

UNITED STATES PATENTS 

